Another Destroyer error?

[Jonbrout]

A bowl contains 1000 tickets numbered between 1 and 1000. What is the probability that a number is between 10 and 90.

The answer says 81/1000!
The****isthis****.jepg

if it's BETWEEN shouldn't it be 78? (89-11=78)

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[Jonbrout]

slow opt forum is slow. zzz.

 

[netmag]

I was never all that great at probability, however if it's inclusive (meaning the 10 ticket and the 90 ticket are supposed to be included) then their result could be right.

If you say it out loud, you can see how there could be an implied inclusiveness. For example, a teacher asking all the kids between 10 and 15 to move over to the left side of the room. It's implied that the 10 and 15 year old kids would move too. The kids wouldn't just stand there and say "well I'm exactly 15 and she said 'between' so technically that wouldn't include me". I would say though that if that's the case, they certainly should have phrased it much clearer considering that it is a test question. It could just be a poorly written example question.

However, even if you assume that it didn't include the #10 and #90 tickets, wouldn't it be 79 instead of the 78 that you came up with?

 

[Vsno123]

@ jonbrout- that's exactly what I answered too (78/100)! Maybe in math terms, the word "between" means something different, like being inclusive. I tried looking it up but I didn't find anything :/

 

[bob12]

yes, agreed

 

[EyEnStein 07]

Is 79/1000 and 81/1000 both choices? That does sound a bit misleading but whether it was inclusive or not, i don't get how you guys got 78.

Doing 89-11 is not the right way to do it, you're actually taking 1 less number.


So just FYI (hopefully this is clear):

You want your "first number" to be 11 and your "last number" to be 89 so:

If its in between (not including 10 and 90) then 11 would be the "first" number, therefore "81" would be the "71st number", to get 81 + 8 = 89

so that means to get from the "71st number" to the "last number" you add 8 and you get that 89 is the 79th number (71+8)


And of course if it were inclusive, then by this reasoning you have 10 and 90 that were not added, so 79+2 = 81.

 

[Vsno123]

EyEnstein you're right lol. I figured this out right after my post. I guess you can just subtract (89-11)+1

 

[netmag]

Not to toot my own horn but I think I mentioned earlier that I thought it would be either 79 or 81 but not 78. I just extrapolated that based on what the Destoyer answer indicated as being correct though.

EyEnstein you're right lol. I figured this out right after my post. I guess you can just subtract (89-11)+1

 

[Vsno123]

Lol my bad. Toot away, netmag! I agree now.

Hopefully the DAT questions won't be this ambiguous